1. Field of the Invention
The present invention relates to a torque detecting apparatus designed appropriately for use in an electric power steering apparatus for a vehicle or the like and comprising a first shaft and a second shaft connected coaxially to each other through a connecting shaft, a permanent magnet fixed to the first shaft, a plurality of soft magnetic members fitted by pressing via a collar with the second shaft and disposed in a magnetic field of the permanent magnet to form a magnetic circuit, and a detector for detecting magnetic flux generated from the soft magnetic members, wherein the soft magnetic members are integrated by molding with synthetic resin, and when a torque is applied to the first shaft or the second shaft, the torque is detected based on an output of the detector.
The present invention also relates to a torque detecting apparatus designed appropriately for use in an electric power steering apparatus for a vehicle or the like and comprising a first shaft and a second shaft connected coaxially to each other through a connecting shaft, a permanent magnet fixed to the first shaft, a plurality of soft magnetic members fixed to the second shaft and disposed in a magnetic field of the permanent magnet to form a magnetic circuit, and a detector for detecting magnetic flux generated from the soft magnetic members, wherein when a torque is applied to the first shaft or the second shaft, the torque is detected based on an output of the detector.
The present invention further relates to a torque detecting apparatus designed appropriately for use in an electric power steering apparatus for a vehicle or the like and comprising a first shaft and a second shaft connected coaxially to each other through a connecting shaft, a permanent magnet fixed to the first shaft, a plurality of soft magnetic members fixed to the second shaft and disposed in a magnetic field of the permanent magnet to form a magnetic circuit, a plurality of auxiliary soft magnetic members magnetically coupled to the soft magnetic members for inducing magnetic flux from the soft magnetic members, and a detector for detecting the magnetic flux induced by the auxiliary soft magnetic members, wherein when a torque is applied to the first shaft or the second shaft, the torque is detected based on an output of the detector; and an electric power steering apparatus equipped with the torque detecting apparatus.
2. Description of the Related Art
An electric power steering apparatus for a vehicle is known, which drives an electric motor to assist the steering thereby relieving the load to a driver. Such an electric power steering apparatus comprises an input shaft connected to a steering member (a steering wheel or a handle), an output shaft connected via a pinion and a rack etc. to wheels to be steered, and a connecting shaft for connecting the input shaft with the output shaft. A torque detecting apparatus detects a torque applied to the input shaft by a torsion angle generated at the connecting shaft, an electric motor for steering assistance which is worked with the output shaft is controlled and driven in response to the detected torque. The torque detecting apparatus in such a electric power steering apparatus is conventionally constructed using a rotation detecting apparatus such as a magnetic detection resolver for detecting the location of rotation by coils or an optical encoder for detecting the location of rotation by the transmission of light.
Also disclosed in Japanese Patent Application Laid-open No. 2003-149062 is a torque sensor, as shown in an exploded perspective view of FIG. 1A, a vertical sectional view of FIG. 1B, and a traverse sectional view of FIG. 1C. The torque sensor comprises an input shaft 1 and an output shaft 2 connected coaxially to each other through a torsion bar 3, an annular 24-pole permanent magnet 5 fixed to the input shaft 1, a magnetic yoke 4 fixed to the output 2 and consisting of a plurality of soft magnetic members 4a and 4b disposed in a magnetic field of the permanent magnet 5 to form a magnetic circuit, two magnetism collecting rings 8, 8 magnetically coupled to the magnetic yokes 4a and 4b for inducting magnetic flux from the magnetic yokes 4a and 4b, and two magnetic sensors 6, 6 (Hall ICs) for detecting the magnetic flux induced by the magnetism collecting rings 8, 8. When a torque is applied to the input shaft 1, the torque is detected based on outputs of the magnetic sensors 6, 6.
The applicants of the present invention have proposed a torque sensor disclosed in Japanese Patent Application Laid-open No. 2005-98821, as shown in FIGS. 1A to 1C, where the magnetic yokes 4a and 4b are integrally molded with synthetic resin while the magnetism collecting rings 8, 8 and the magnetic sensors 6, 6 are integrally molded with synthetic resin with respect to the torque sensor described above.
The torque sensor described above has magnetic yokes 4a and 4b which are integrally molded with synthetic resin and fitted via a not-shown collar with the output shaft 2 by pressing. Since the collar is made of a magnetic material (S43C), the collar may affect the above magnetic circuit. Also, when the output shaft is fitted by pressing with the collar, scraping dusts may generate, which then affect the magnetic circuit.
Also, in the torque sensor described above, two steps are needed for molding the magnetism collecting rings 8, 8, the magnetic sensors 6, 6, and the circuit board with the synthetic resin. More specifically, the first step is conducted to mold the magnetic sensors 6, 6 and the circuit board as electronic components with flexible synthetic resin (for example, hot melt). At the second step, the magnetism collecting rings 8, 8 are molded with rigid synthetic resin (for example, PBT). This relieves the adverse effect of the rigid synthetic resin over the electronic components.
However, the synthetic resin used at the first step fails to provide a desired physical strength of bonding with the circuit board etc. When applied to heat many times and repeatedly expanded and contracted, the synthetic resin will detach from the circuit board etc. and finally a gap 30 will be generated between the synthetic resin and the circuit board 19, as shown in FIG. 2.
Moreover, the torque sensor described above requires a harness and a connector for connection with the controller of the electronic power steering apparatus, thus increasing the component cost and the number of the components.